blktap2: Fix sysfs handling of blktap2

The pause and unpause paths are currently broken due to a missing
slash. I took advantage of the opportunity to remove code repetition,
repeated strings that should point to the proper constants, etc

From: Andres Lagar Cavilla <andreslc@cs.toronto.edu>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

tools/python/xen/xend/XendDomainInfo.py

@@ -60,6 +60,7 @@ from xen.xend.xenstore.xswatch import xswatch
 from xen.xend.XendConstants import *
 from xen.xend.XendAPIConstants import *
 from xen.xend.server.DevConstants import xenbusState
+from xen.xend.server.BlktapController import TAPDISK_DEVICE, parseDeviceString
 
 from xen.xend.XendVMMetrics import XendVMMetrics
 
@@ -528,18 +529,18 @@ class XendDomainInfo:
         try:
             if(self.domid):
                 # get all blktap2 devices
-                dev =  xstransact.List(self.vmpath + 'device/tap2')
+                dev =  xstransact.List(self.vmpath + '/device/tap2')
                 for x in dev:
                     path = self.getDeviceController('tap2').readBackend(x, 'params')
-                    if path and path.startswith('/dev/xen/blktap-2'):
-                        #Figure out the sysfs path.
-                        pattern = re.compile('/dev/xen/blktap-2/tapdev(\d+)$')
-                        ctrlid = pattern.search(path)
-                        ctrl = '/sys/class/blktap2/blktap' + ctrlid.group(1)            
-                        #pause the disk
-                        f = open(ctrl + '/pause', 'w')
-                        f.write('pause');
-                        f.close()
+                    if path and path.startswith(TAPDISK_DEVICE):
+                        try:
+                            _minor, _dev, ctrl = parseDeviceString(path)
+                            #pause the disk
+                            f = open(ctrl + '/pause', 'w')
+                            f.write('pause');
+                            f.close()
+                        except:
+                            pass
         except Exception, ex:
             log.warn('Could not pause blktap disk.');
 
@@ -557,19 +558,20 @@ class XendDomainInfo:
         """
         try:
             if(self.domid):
-                dev =  xstransact.List(self.vmpath + 'device/tap2')
+                dev =  xstransact.List(self.vmpath + '/device/tap2')
                 for x in dev:
                     path = self.getDeviceController('tap2').readBackend(x, 'params')
-                    if path and path.startswith('/dev/xen/blktap-2'):
-                        #Figure out the sysfs path.
-                        pattern = re.compile('/dev/xen/blktap-2/tapdev(\d+)$')
-                        ctrlid = pattern.search(path)
-                        ctrl = '/sys/class/blktap2/blktap' + ctrlid.group(1)
-                        #unpause the disk
-                        if(os.path.exists(ctrl + '/resume')):                  
-                            f = open(ctrl + '/resume', 'w');
-                            f.write('resume');
-                            f.close();
+                    if path and path.startswith(TAPDISK_DEVICE):
+                        try:
+                            #Figure out the sysfs path.
+                            _minor, _dev, ctrl = parseDeviceString(path)
+                            #unpause the disk
+                            if(os.path.exists(ctrl + '/resume')):                  
+                                f = open(ctrl + '/resume', 'w');
+                                f.write('resume');
+                                f.close();
+                        except:
+                            pass
 
         except Exception, ex:
             log.warn('Could not unpause blktap disk: %s' % str(ex));

tools/python/xen/xend/server/BlktapController.py

@@ -235,9 +235,7 @@ class Blktap2Controller(BlktapController):
         self.waitForBackend_destroy(backpath)
 
         #Figure out the sysfs path.
-        pattern = re.compile('/dev/xen/blktap-2/tapdev(\d+)$')
-        ctrlid = pattern.search(path)
-        ctrl = '/sys/class/blktap2/blktap' + ctrlid.group(1)
+        minor, dev, ctrl = parseDeviceString(path)
 
         #Close out the disk
         f = open(ctrl + '/remove', 'w')